1. Field of the Invention
This invention relates to a holding method of a plate-like specimen in a noncontact condition, a fluid treatment method of a specimen surface using the holding method, and systems for carrying out the methods and in particular to a holding method of a plate-like specimen in a noncontact condition, a fluid treatment method of a specimen surface using the holding method, and systems for carrying out the methods appropriate for a thin-film device manufacturing process, etc., requiring cleanness.
2. Description of the Related Art
In recent years, thin-film devices such as semiconductors and liquid crystal displays have advanced in microstructures, and demands for high performance of their manufacturing technologies and a highly clean manufacturing process have increased. For example, thin-film devices of semiconductors require that the foreign material with the size 0.3 .mu.m or more should be removed, that the adsorptive ion amount should be less than 10.sup.9 atoms/cm.sup.2, and that the thickness of an oxide film formed on exposure to air should be 1 nm or less. Although thin-film device substrates at the manufacturing time become large-sized, demands for preventing an increase in the system volume and low costs of systems also increase. Further, drastic improvement in the processing speed is desired.
A method of processing substrate specimens (simply called specimens) one at a time, called single wafer processing, is available as one specific measure for meeting the demands; for example, it is put into practical use in a film formation step, etc., of a semiconductor manufacturing process.
However, the state-of-the-art single wafer processing system does not satisfy all the demands. This point will be discussed separately for each of specimen holding and treatment.
The main specimen holding methods in single wafer processing include a method of placing a specimen on a holder, a method of adsorbing and holding a specimen by vacuum chuck, and a method of mechanically grasping a specimen end. However, in every method, the holder comes in direct contact with the specimen. Thus, the contact part of the specimen is contaminated, leading to one source of an increase in the defective product occurrence rate. Since spatial restrictions for an operation drive and power transmission path are placed on the holder and transfer device, the treatment system becomes larger and complicated.
A specific example related to the single wafer processing method is given in Japanese Patent Laid-Open No. Hei 4-287922, which will be hereinafter called the first conventional example, wherein a specimen is fixed by substrate rotation means (spin chuck) and fluid is jetted to the specimen surface for surface treatment while the specimen is rotated mechanically.
Available as a method for avoiding the above-mentioned disadvantage is a specimen noncontact holding method using the Bernoulli effect of fluid, which will be hereinafter referred to as Bernoulli holding or Bernoulli chuck, as described in Japanese Patent Publication No. Sho 53-29550, which will be hereinafter called the second conventional example.
FIG. 1A is a sectional view of the main part showing a typical structure of Bernoulli holding. In the second conventional example, a specimen 10 having a plane and a flat plate (holder) 20 having a fluid supply hole 30 made on a surface are opposed to each other in parallel and the specimen 10 is noncontact-held by using negative pressure p between the specimen 10 and the holder 20 occurring when fluid 100 is supplied from the fluid supply hole 30, namely, the known Bernoulli effect. F in the figure denotes a fluid jet force that the specimen 10 receives when the fluid is jetted.
The principle of negative pressure p occurring between the specimen 10 and the holder 20 is known by the Bernoulli's theorem and therefore will not be discussed in detail here. Assuming that the negative pressure p is an attractive force, the fluid jet force becomes a repulsive force. The specimen 10 is noncontact-held by the holder 20 at a position where the attractive force and repulsive force and gravity caused by the specimen weight are balanced.
The Bernoulli holding is true as in FIG. 1A if the positional relationship between the specimen 10 and the holder 20 is inverted with respect to a top as shown in FIG. 1B.
The Bernoulli holding, which is noncontact holding, enables low contaminated specimen holding. The holding method also enables miniaturization of the system because a large-scaled drive and a power transmission path need not be used.
However, in the conventional method as described above, a force for inhibiting a lateral position shift of a specimen does not act, so that a position shift is prone to occur, To solve the problem, a method of mechanically bringing a stopper into contact with a specimen or a method of detecting a position shift and correcting it can be used. However, the former method does not provide complete noncontact holding because the position shift prevention means, etc., comes in partial contact with the specimen. The position shift prevention means in the latter method leads to a complicated system; it is hard to miniaturize.
Available as another noncontact holding method is a method of providing a fluid jet substrate on both or either of the top and bottom between which a wafer as a specimen is sandwiched and rotating the wafer with it picked up for treatment, which will be hereinafter referred to as the third conventional example, as described in Japanese Patent Laid-Open No. Sho 60-74438 and Japanese Patent Publication No. Hei 4-69420.
In the related arts, a force for inhibiting vertical and lateral position shifts of the wafer does not act. Further, the wafer has a chipped part called orientation flat and is asymmetric with respect to an axis. Thus, the fluid jet amount needs to be accurately controlled to enable packing up and rotation of the wafer.
That is, means for sensing the wafer position and control means for determining the point, direction, and amount of jetting fluid are required as described in Japanese Patent Laid-Open No. Hei 5-211225. This results in a large-scaled, complicated, and high-cost system, which is contrary to the present demands as described above.
Since gas can also be handled as incompressible fluid like liquid in an area in which the gas flow velocity is about a half of acoustic velocity (173 m/s) or less, it is well known from the fluid mechanics field that similar discussion can be applied in the related arts regardless of whether fluid is gas or liquid.
However, the art described in the first conventional example provides the holding method in which the holder comes in direct contact with a specimen, and contamination of the contact part of the specimen cannot be avoided. Since the specimen is held, washed, and dried by separate mechanisms, the system volume becomes large.
The art described in the second conventional example, which provides the holding method via fluid, is more excellent in the system volume and cleanness than the first conventional example, but a projection located on the outer surface of a holding plate to stabilize the holding position comes in contact with a specimen. Therefore, the contamination problem of the contact part of the specimen remains unsolved.
The art described in the third conventional example picks up and rotates a specimen by jetting wash liquid; it does not have means for ensuring that the specimen holding position is stable. Thus, the specimen is placed out of position due to an uneven jet caused by vibration, ripple, uneven rotation, pressure change, involved bubbles, etc., of a pump jetting wash liquid. In a remarkable case, the specimen collides with the side wall connecting the upper and lower jet parts or the upper or lower jet part. The specimen may be broken by the collision, broken pieces causing contamination. Particularly, a semiconductor wafer, which has a notch called orientation flat, is not a true circle and the rotation center and center of gravity differ. Thus, in picking up and rotation by the method, a position shift is prone to occur.
As described above, the related arts do not provide a system meeting the present demands, namely, a system which can stably hold a specimen in a noncontact condition, provide high cleanness by treatment, be small-sized and inexpensive because of few mechanical features, inhibit oxide film growth because of nonexposure to air, and perform high-speed treatment because of fast flow velocity of treatment fluid.